Review of Seafarer 31 Mk I

The hull is made of fibreglass. Generally, a hull made of fibreglass requires only a minimum of maintenance during the sailing season. And outside the sailing season, just bottom cleaning and perhaps anti-fouling painting once a year - a few hours of work, that's all.

The boat equipped with a masthead rig. The advantage of a masthead rig is its simplicity and the fact that a given sail area - compared with a fractional rig - can be carried lower and thus with less heeling moment.

The Seafarer 31 Mk I is equipped with a long keel. A long keel provide a better directional stability than a similar boat with a fin keel; on the other hand, better directional stability means also that the boat is more difficult to handle in a harbour with less space.

The keel is made of lead. Compared with iron, lead has the advantage of being 44% heavier, which allows a smaller keel and hence less water resistance and higher speed.

The boat can enter most marinas as the draft is just about 1.52 - 1.62 meter (4.99 - 5.29 ft) dependent on the load. See immersion rate below.

The boat is typically equipped with an inboard Universal Atomic 4 gasoline engine at 30.0 hp (22 kW), which gives a max speed about 6.3 knots.

What is Capsize Screening Formula (CSF)?

The capsize screening value for Seafarer 31 Mk I is 1.70, indicating that this boat could - if evaluated by this formula alone - be accepted to participate in ocean races.

What is Theoretical Maximum Hull Speed?

The theoretical maximal speed of a displacement boat of this length is 6.1 knots. The term "Theoretical Maximum Hull Speed" is widely used even though a boat can sail faster. The term shall be interpreted as above the theoretical speed a great additional power is necessary for a small gain in speed.

The immersion rate is defined as the weight required to sink the boat a certain level. The immersion rate for Seafarer 31 Mk I is about 114 kg/cm, alternatively 641 lbs/inch.
Meaning: if you load 114 kg cargo on the boat then it will sink 1 cm. Alternatively, if you load 641 lbs cargo on the boat it will sink 1 inch.

What is Motion Comfort Ratio (MCR)?

The Motion Comfort Ratio for Seafarer 31 Mk I is 31.2.

Comparing this ratio with similar sailboats show that it is more comfortable than 86% of all similar sailboat designs. This is a comfort value significantly above average.

What is L/B (Length Beam Ratio)?

The l/b ratio for Seafarer 31 Mk I is 3.57.

Compared with other similar sailboats it is slimmer than 85% of all other designs. It seems that the designer has chosen a significantly more speedy hull design.

What is a Ballast Ratio?

The ballast ratio for Seafarer 31 Mk I is 38%.

This ballast ratio shows a righting moment that is higher than 34% of all similar sailboat designs. A righting moment (ability to resist heeling) just below average.

What is Displacement Length Ratio?

The DL-ratio for Seafarer 31 Mk I is 424 which categorizes this boat among 'heavy cruisers'.

2% of all similar sailboat designs are categorized as heavier. A heavy displacement combined with smaller water plane area has lower acceleration and is more comfortable.

What is SA/D (Sail Area Displacement ratio)?

The SA/D for Seafarer 31 Mk I with ISO 8666 reference sail is 13.3, with a 135% genua the SA/D is 15.6.

The SA/D ratio indicates that it is faster than 14% of all similar sailboat designs in light wind.

The Seafarer 31 Mk I has more rig than 54% of all similar sailboats, which indicates that the boat is slightly overrigged.

When buying anti-fouling bottom paint, it's nice to know how much to buy. The surface of the wet bottom is about 13m² (139 ft²).
Based on this, your favourite maritime shop can tell you the quantity you need.

Note: If you use a paint roller you will need more paint than if you use a paintbrush.

Dimensions of sail.

Are your sails worn out? You might find your next sail here: Sails for Sale

If you need to renew parts of your running rig and is not quite sure of the dimensions, you may find the estimates computed below useful.

This section shown boat owner's changes, improvements, etc. Here you might find inspiration for your boat.

Do you have changes/improvements you would like to share? Upload a photo and describe what to look for.

We are always looking for new photos. If you can contribute with photos for Seafarer 31 Mk I it would be a great help.

If you have any comments to the review, improvement suggestions, or the like, feel free to contact us. Criticism helps us to improve.

[Ref 1]: ISO 8666 Small craft — Principal data.
[Ref 3]: ISO 12215-5 Small craft — Hull construction and scantlings.